1. Field of the Invention
This invention relates to a pull cord device and a window covering including the same, more particularly to a pull cord device which employs a cord-release controlling member to control a locking wheel so as to permit or prevent rotation of a cord spool for moving or positioning a base rail relative to a header rail of the window covering.
2. Description of the Related Art
A conventional “cordless” window covering, such as those disclosed in U.S. Pat. Nos. 6,079,471 and 6,289,965, generally includes a spring motor to raise or lower slats between header and base rails of the window covering. The spring motor includes a take-up drum, a drive drum, and a coil spring interconnected between the take-up and drive drums, with its biased or relaxed position being wound upon the take-up drum. The coil spring can be of constant or variable force, and cooperates with a friction adjuster to balance the weight of the base rail and accumulated slats on the base rail so as to position the base rail at a desired height. However, since windows have different dimensions, window coverings are required to have different sizes. Hence, the weights of the base rails and slats of different window coverings vary. Consequently, the spring motors mounted on the window coverings are required to have coil springs with different biasing forces, and matching friction adjusters with different frictional forces, thereby rendering mass production of window coverings difficult.
Referring to FIGS. 1 and 2, a cordless blind disclosed in U.S. Pat. No. 6,024,154 is shown to include a header rail 1, a base rail 2, a plurality of slats 3, two pull cords 4, a winding member 5, and a positioning member 6. The winding member 5 includes a housing 501, two cord retrieving and winding wheels 502 rotatably mounted in the housing 501, and two coil springs 503 connected to the housing 501 and the respective cord retrieving and winding wheels 502. Each of the cord retrieving and winding wheels 502 has a winding portion 504 for winding the respective pull cord 4, and a toothed retaining portion 505. The positioning member 6 has a retaining body 601 and a plurality of springs 602 abutting against the housing 501 and the retaining body 601. The retaining body 601 has two racks 603 disposed to respectively mesh with the toothed retaining portions 505 of the cord retrieving and winding wheels 502. When the retaining body 601 is pressed to cause the racks 603 to disengage from the toothed retaining portions 505, a further pressing force can initiate the wheels 502 to wind the pull cords 4 by means of the coil springs 503 so as to raise the slats 3. On the contrary, when the base rail 2 is pulled downwardly by hand to lower the slats 3 and is then released, the racks 603 will return to their original position by means of the springs 602 to mesh with the toothed retaining portions 505 so as to stop the rotation of the wheels 502, the base rail 2 is thus positioned at a desired height.
Such a cordless blind has the following drawbacks:
1. As shown in FIGS. 2 and 3, since the winding and positioning members 5, 6 are located at a central portion of the base rail 2, and since the user usually uses one hand to press the retaining body 601 and press or pull the base rail 2, the wheels 502 are not able to wind the pull cords 4 evenly thereon. Thus, the base rail 2 tends to slant to one side.
2. Since lower ends of the pull cords 4 are wound on the wheels 502, once the base rail 2 slants to one side as shown in FIG. 3, the user has to press the retaining body 601 with one hand, and pull a higher part of the base rail 2 with the other hand. The adjusting operation as such is relatively inconvenient to conduct.